1. Field of Inventions
The present inventions relate generally to electrophysiology probes such as catheters and surgical probes and, more particularly, to electrodes for use with electrophysiology probes.
2. Description of the Related Art
Catheters, surgical probes and related electrophysiological devices (together referred to herein as "electrophysiological probes" or "probes") are used today in diagnostic and therapeutic medical procedures that require surgical or minimally invasive access to targeted tissue areas within interior regions of the body. The probes include support bodies that typically carry an array of linearly spaced electrodes at the distal end thereof. Probe power control systems that allow physicians to individually control the power applied to the electrodes in such multiple electrode probes are also available. One example of such a system is disclosed in U.S. Pat. No. 5,545,193.
Precise positioning of the electrodes is of paramount importance in all probe-based procedures. However, the need for careful and precise positioning of the electrodes is especially critical during certain procedures concerning the heart. These procedures, called electrophysiological therapy, are becoming more widespread for treating cardiac rhythm disturbances. Cardiac tissue coagulation (sometimes referred to as "ablation"), where therapeutic lesions are formed in cardiac tissue, is one procedure in which the ability to precisely position the electrodes is especially important. During catheter-based procedures, a physician steers the catheter through a main vein or artery into the region of the heart that is to be treated. In surgical probe-based procedures, the distal portion of the probe is inserted through the patient's chest and directly into the heart. The physician must then precisely place the linear array of electrodes near the cardiac tissue that is to be coagulated. Fluoroscopic imaging in often used to identify anatomic landmarks within the heart and to position the electrodes relative to the targeted tissue region. Once the electrodes are properly positioned, the physician directs energy from the electrodes to the tissue to form a lesion.
Rigid ring-shaped electrodes were originally used in electrophysiological probes. In recent years, coil electrodes have been introduced in order to increase the flexibility of the distal portion of the probes, thereby enabling the physician to more precisely control the position and shape of the distal portion of the probe and to achieve superior tissue contact. The metals used to manufacture conventional coil electrodes have been heretofore selected according to certain mechanical properties, the primarily property being resiliency. A relatively high level of resiliency is required during the various manufacturing processes, such as coil winding and the mounting of coils onto a probe, because relatively resilient material returns to its original shape after being manipulated during manufacturing, as compared to softer, less resilient materials such as platinum or gold which can be permanently deformed during manufacturing. Relatively resilient materials are also more durable than softer, less resilient materials. Another desirable mechanical property is stiffness. Accordingly, coil electrodes have been formed from relatively resilient and stiff materials and, more specifically, from stainless steel.
The radiopacity of stainless steel is, however, relatively low. Thus, while otherwise superior to coil electrodes formed from less resilient materials such as platinum or gold, stainless steel coil electrodes are difficult to visualize using fluoroscopic imaging techniques. The low visibility of conventional stainless steel coil electrodes makes it difficult to properly position the distal portion of the probe. It is also difficult to differentiate between individual coil electrodes which, in turn, makes individual control of the electrodes difficult even when the distal portion of the probe is properly positioned. The difficulties associated with electrode differentiation are further compounded when the probe includes a relatively large number of electrodes.
One proposed solution to this problem has been to include radiopaque markers on probes in addition to the electrodes. The inventors herein have determined that this proposed solution is less than optimal because the electrodes must be closely spaced in order to insure reliable creation of contiguous lesions between adjacent electrodes. The close spacing precludes the placement of radiopaque markers between the electrodes.